This invention generally relates to semiconductor processing and, in particular, to a method of modifying one or more properties of a thin film composite material by ion implantation. These properties may pertain to the bulk or to the surface of the thin film and may include resistivity, temperature coefficient of resistance, optical transparency, transparency in other non-optical wavelengths or interfacial properties with other materials.
Thin film composite materials, such as thin film resistors, are employed in many integrated circuits. These resistors are used in integrated circuits to implement the desired functionally of the circuit, including biasing of active devices, serving as voltage dividers, assisting in impedance matching, etc. They are typically formed by deposition of a resistive material on a dielectric layer, and subsequently patterned to a desired size and shape. Deposition of resistive material can be performed by any deposition means, such as by sputtering. Often, a thin film resistor is subjected to a heat treatment process which may be part of the overall integrated circuit process. This heat process, often referred to as xe2x80x9cannealingxe2x80x9d, may improve thin film material stability and may alter some, none or all of the various other properties to various degrees. In particular, annealing may alter film resistivity and temperature coefficient of resistance.
In general, the properties of the as-deposited thin film composite material are fixed. That is, when deposited the thin film material will exhibit particular electrical, optical, thermal and physical properties which may or may not be altered by heat treatment. These properties may include the sheet resistance, temperature coefficient of resistance, optical transparency, transparency in other non-optical wavelengths, physical properties, and other properties. Generally, these properties are set by the material composition of the composite or mosaic target used to sputter the thin-film material on the surface of the wafer. The degree of alteration of these properties by annealing does not occur in a proportionate manner, that is, some properties may be altered by a large factor while others may be altered significantly less.
However, there is a need to alter some or all of these properties after the thin film composite materials is deposited on the surface of the wafer. Annealing at a particular temperature may not be possible due to inherent limitations of the integrated circuit or the degree of alteration may not be as much as required. For instance, there may be a need to modify the sheet resistance of the deposited thin film material more than can be achieved by annealing without modifying other properties. Similarly, there may be a need to modify the temperature coefficient resistance of the annealed film alone. There may be a further need to modify other electrical, thermal, optical and physical properties of the deposited thin film composite material. Additionally, there may be a need to perform these modifications on only selected regions of the deposited Mm Furthermore, there may be a need to modifiat two or more properties of the deposited thin film composite material in respectively different manners with one or more process steps.
These needs and others are met by the method of modifying properties of deposited thin-film resistive material in accordance with the invention.
An aspect of the invention relates to a method of modifying a layer of thin film composite material to achieve one or more desired properties for the thin film layer which cannot be achieved by heat treatment at all practical temperatures of operation allowable by particular integrated circuit processes. In particular, the thin film composite material is subjected to an ion implantation process. Depending on the doping species, the doping concentration, the doping energy, and other ion implantation parameters, one or more properties of the deposited thin film layer can be modified. Such properties may include electrical, optical, thermal and physical properties. These properties may be modified linearly or non-linearly. For instance, the sheet resistance and/or the temperature coefficient of resistance of the thin film composite material may be increased or decreased by appropriately implanting ions into the material. The ion implantation can be applied globally in order to modify one or more properties of the entire thin film composite layer. Alternatively, the ion implantation can be applied regionally in order to modify the thin film composite material at a particular region, not modify the thin film composite material at a second region, and/or modify the thin film composite material in another way at a third region by performing a different ion implantation on the third region.
Other aspects, features, and techniques of the invention will become apparent to one skilled in the relevant art in view of the following detailed description of the invention.